Powder coating composition, method for the curing thereof, and articles derived therefrom

ABSTRACT

A powder coating composition includes an epoxy resin and a styrene-maleic anhydride copolymer having a glass transition temperature less than 105° C. The compositions provide low gloss finishes at low curing temperatures, as well as consistent gloss over a wide range of curing temperatures.

CROSS REFERENCE TO RELATED PATENT APPLICATIONS

This is a non-provisional application of prior pending U.S. provisionalapplication Ser. No. 60/328,587 filed Oct. 11, 2001.

BACKGROUND

The present invention relates to a powder coating composition capable ofproviding a matte or low gloss finish on a variety of substrates. Thegloss of a cured powder coating is typically described using termsincluding “matte”, “low gloss”, and “mid gloss” finishes. In general,gloss is expressed as a percentage of intensity of the reflected lightwith respect to the intensity of the incident light at a specified anglebetween the incident light beam and the planar test surface. The terms“matte”, “low gloss”, and “mid gloss” are defined herein according glossmeasured according to ASTM D523 at an angle of 60°. Specifically, a“matte” finish has a 60° gloss less than 20 units; a “low gloss” finishhas a 60° gloss of 20 to less than 40 units; and a “mid gloss” finishhas a 60° gloss of 40 to less than 60 units.

Gloss reduction in powder coatings may be achieved by producing a finesurface morphology that scatters incident light, resulting in a lowerpercentage of reflected light. This low percentage of reflected lightgives the appearance of matte or reduced gloss. A variety of methodshave been developed to provide low gloss powder coatings, including theincorporation of fillers or extenders, the incorporation of incompatibleingredients such as waxes, dry blending of different formulations, andthrough the incorporation of matting agents.

The incorporation of fillers or extenders has been used to produce glossin the mid-gloss range, however this technique does not readily providefor coatings to be produced with a smooth matte or low gloss finish.Also, the incorporation of fillers can lead to coatings with reducedphysical properties including impact, flexibility, and adhesion due toreduced binder concentrations.

The incorporation of incompatible ingredients such as waxes is alsocommonly used to produce mid gloss finishes. As with the incorporationof extenders, this technique does not readily provide for coatings withmatte or low gloss. Incorporation of waxes often leads to the formationof a surface film as waxes migrate over time, and removal of the surfacefilm can expose a glossy surface underneath.

Dry blending of two powders that have different reactivities or areimmiscible has been described in, for example, U.S. Pat. No. 3,842,035to Klaren. Dry blending requires an additional manufacturing step andthe resulting dry blended components can separate over time in aconventional powder coating application and recycle process. Theseparation of components during the application and recycle process canyield fluctuations in gloss and curing efficiency.

The incorporation of matting agents has also been used to provide acoating with matte or low gloss appearance. The underlying process hasbeen described as one of competing reactions or varying rates ofseparate reactions. The use of reactive matting agents is described in,for example, European Patent Application Nos. 72,371 A1 to Holdereggeret al., and 44,030 A1 to Gude et al.; European Patent Nos. 165,207 B1and 366,608 B1 to Lauterbach; U.S. Pat. No. 5,684,067 to Muthiah et al.,U.S. Pat. No. 5,786,419 to Meier-Westhues et al.; D. H. Howell in “TheTechnology, Formulation and Application of Powder Coatings”, J. D.Sanders, Ed., John Wiley and Sons in association with SITA TechnologyLimited: London, England 2000. Vol. 1, pages 152-178; C. Grob and C.Rickert (2000) Water-Borne, Higher-Solids, and Powder CoatingsSymposium, New Orleans, 1-3 Mar. 2000, pp 337-349; P. A. Chetcuti, B.Dreher, and P. Gottis, Mod Paint Coatings (1995), volume 85, no. 7,pages 28-32; J. J. Salitros and R. Patarcity, Proc. Water-Borne,Higher-Solids, Powder Coat. Symp. (1992), 19th, pages 517-526; and J.Schmidhauser and J. Havard, Proc. Int. Waterborne, High-Solids, PowderCoat. Symp. (2001), 28th, 391-404.

Gloss has been lowered in epoxy powder coating systems by using reactivematting agents such as cyclic amidines and amidine salts as described,for example, in European Patent Application No. 44,030 to Gude et al.,and in Ciba-Geigy Product Literature “Matting Agents/Hardeners forPowder Coatings”. This is commonly known as “veba” technology.

Another approach is the addition of acid anhydride containing materials,addition of polyacids, or by dry blending two powder coatings withdifferent reactivities as described in U.S. Pat. No. 3,842,035 toKlaren. Howell, cited above, refers to the incorporation of reactivematting in powder coatings to achieve low gloss and states that glosslevel of less than 20% are attainable but depend on the curingconditions, which have to be carefully controlled in order to ensurereproducibility.

Examples of acid functional reactive matting agents used in epoxysystems and polyester/epoxy hybrid systems include styrene maleicanhydride copolymers or esterified styrene maleic anhydride copolymersas described in the Salitros et al. and Schmidhauser et al. referencescited above. The styrene-maleic anhydride copolymers are described asfunctioning as matting agents at cure temperatures of at least 400° F.in polyester/epoxy hybrid systems.

There remains a need for a coating composition that provides low glossat low curing temperatures and consistently provides low gloss or mattegloss over a broad temperature range.

BRIEF SUMMARY

The above-described and other drawbacks and disadvantages of the priorart are alleviated by a curable powder coating composition, comprising:an epoxy thermosetting resin; and a matting agent selected fromstyrene-maleic anhydride copolymers having a glass transitiontemperature less than 105° C.

Other embodiments, including a method of forming a cured powder coating,are described in detail below.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

One embodiment is a powder coating composition comprising: an epoxythermoset resin; and a matting agent selected from styrene-maleicanhydride copolymers having a glass transition temperature less than105° C.

The composition comprises an epoxy thermoset resin, hereinafter referredto as an epoxy resin. The glass transition temperature (T_(g)) of theepoxy resins is preferably high enough that the particles do not fusetogether or sinter at temperatures likely to be encountered duringtransportation and storage. Preferably, the T_(g) is at least 50° C.,more preferably at least 60° C.

Suitable epoxy resins include those containing aliphatic or aromaticbackbones with oxirane functionality. They may be formed by the reactionof a diol and a halohydrin. Examples include the diglycidyl ethercondensation polymers resulting from the reaction of epichlorohydrinwith a bisphenol in the presence of an alkaline catalyst. Bisphenol A ismost commonly used but the bisphenols B, F, G, AF, S and H are alsosuitable. Generally, the bisphenol A type epoxies may be of the type 1to type 9 form, with the low viscosity type 3 or less epoxy resins beingpreferred. By controlling the operating conditions and varying the ratioof the reactants, products of various equivalent weights can be made. Itmay be preferred that the epoxide equivalent weight (EEW) may be 400 to2,250 atomic mass units (AMU). Within this range, an EEW of at least 550AMU may be preferred. Also within this range, an EEW of up to 1,100 AMUmay be preferred, and an EEW of up to 750 may be more preferred.

Epoxy resins are available from a wide variety of commercial sources.Useful epoxy resins include the bisphenol A epoxy resins available fromVantico as ARALDITE® GT-7004, GT-7013 (type 3), GT-7014, GT-7072 (type2), GT-7074, GT-7097, and the like. Bisphenol A epoxy resins furtherinclude those available from Shell Chemical Company as EPON® 1007F,EPON® 1009F, EPON® 1004, and the like. Suitable epoxy resins furtherinclude the epoxy phenol novolac resins available from Vantico asARALDITE® GT-7220, and the epoxy cresol novolac resins available fromVantico as ARALDITE® GT-6259.

The powder coating composition further comprises a styrene-maleicanhydride resin having a glass transition temperature (T_(g)) less than105° C. A T_(g) of 40° C. to 105° C. is preferred. Within this range,the T_(g) may preferably be at least 45° C. Also within this range, theT_(g) may preferably be up to 100° C., more preferably up to 90° C., yetmore preferably up to 80° C. The styrene-maleic anhydride resin maypreferably have a mole ratio of styrene:maleic anhydride of 1:1 to 4:1.

Suitable styrene-maleic anhydride resins include unmodifiedstyrene-maleic anhydride resins, partially or fully monoesterifiedstyrene-maleic anhydride resins (in which one of the two carbonyls oneach maleic anhydride is present as a partially or fully esterifiedcarboxylic acid and the other is present as a free carboxylic acid),partially or fully diesterified styrene-maleic anhydride resins (inwhich both of the carbonyls on each maleic anhydride are present aspartially or fully esterified carboxylic acids), and mixtures comprisingat least one of the foregoing resins. Preferred ester groups may beformed by reaction of an unmodified styrene-maleic anhydride with analcohol having 4 to 24 carbon atoms.

The acid number of the styrene/maleic anhydride resin is preferably 100to 320 mg KOH/g. Within this range, the acid number may preferably be atleast 110 mg KOH/g. Also within this range, the acid number maypreferably be up to 210 mg KOH/g.

Suitable styrene-maleic anhydride resins include, for example, thepartially monoesterified styrene-maleic anhydride copolymer obtained asSMA® 1440F from Sartomer, having a styrene:maleic anhydride mole ratioof 1:1, a glass transition temperature of 55° C., an acid number of165-205, 55-75% monoesterification, and melt viscosities of 300 poise at160° C., 110 poise at 180° C., and 70 poise at 200° C.; the partiallymonoesterified styrene-maleic anhydride copolymer obtained as SMA®X.10840 from Sartomer, having a styrene:maleic anhydride mole ratio of1:1, a number average molecular weight of 2,640 AMU, a weight averagemolecular weight of 5,600 AMU, a glass transition temperature of 85° C.,an acid number of 240, 65% monoesterification, and viscosities of 1,700poise at 160° C., 420 poise at 180° C., and 140 poise at 200° C.; thepartially monoesterified styrene-maleic anhydride copolymer obtained asSMA® X.11825 from Sartomer, having a styrene:maleic anhydride mole ratioof 1:1, a glass transition temperature of 110° C., an acid number of315, 25% monoesterification, a weight average molecular weight of 3,200AMU, and a number average molecular weight of 6,800 AMU; and thepartially esterified styrene-maleic anhydride copolymer obtained as SMA®X.11850 from Sartomer, having a styrene:maleic anhydride mole ratio of1:1, a glass transition temperature of 90° C., an acid number of 215,50% monoesterification; a number average molecular weight of 3,800 AMU,and a weight average molecular weight of 8,300 AMU. Preferredstyrene-maleic anhydride resins include the partially monoesterifiedstyrene-maleic anhydride copolymer obtained as SMA® 1440F from Sartomer.

The composition may comprise the styrene-maleic anhydride resin in anamount of 3 to 30 parts by weight per 100 parts by weight of the epoxyresin. Within this range, the styrene-maleic anhydride resin amount maypreferably be at least 5 parts by weight. Also within this range, thestyrene-maleic anhydride amount may preferably be up to 20 parts byweight.

The composition may, optionally, comprise a curing agent. Suitablecuring agents include, for example, imidazoles, amines, and phenolics.Although the resins are self curing, the addition of a curing agent maybe useful to raise the curing rate to a commercially desirable value.

Suitable curing agents for epoxy resins include epoxy adducts of animidazole having the formula:

wherein R¹-R⁴ are each independently hydrogen, C₁-C₁₂ alkyl, C₆-C₁₈aryl, C₇-C₁₈ arylalkyl, C₇-C₁₈ alkylaryl, or the like. Examples ofsuitable imidazoles include imidazole, 2-methyl imidazole, and 2-phenylimidazole. The imidazoles themselves are commercially available as, forexample, 2-phenyl imidazole from the SKW Chemical Co. Suitable adductsof such imidazoles with a bisphenol A epoxy resin are availablecommercially as, for example, EPON® P-101 from Resolution, and ARALDITE®HT-3261 from Vantico. Mixtures of imidazole adducts may be used. Whilenot wishing to be bound by any particular theory, Applicants believethat the imidazole adducts catalyze curing of epoxy resins by an openingof the epoxy ring that results in the epoxy oxygen bonding to the C═Nbond of the imidazole ring. The adducted imidazole acts as a catalyst,moving from one epoxy group to another as it facilitates epoxy ringopening and cure reactions. The imidazoles are, in themselves, theoperative catalysts but they tend to be insoluble in epoxy resins. Thus,adducting an imidazole to an epoxy resin increases its compatibilitywith the epoxy system.

Suitable curing agents for epoxy resins further include organoboratesalts of the formulae:

wherein Z is P, As, or N; each R⁵ is independently C₁-C₁₂ alkyl, C₂-C₁₂alkenyl, C₆-C₁₈ aryl, C₇-C₁₈ arylalkyl, C₇-C₁₈ alkylaryl, or the like;and each R⁶ is independently C₁-C₁₂ alkyl, C₆-C₁₈ aryl, C₇-C₁₈arylalkyl, C₇-C₁₈ alkylaryl, Br, Cl, I, F, or the like; and each R⁷ isindependently hydrogen, C₁-C₁₂ alkyl, C₂-C₁₂ alkenyl, C₆-C₁₈ aryl,C₇-C₁₈ arylalkyl, C₇-C₁₈ alkylaryl, C₂-C₁₂ acyl, aldehyde, carboxylate,cyano, nitro, or the like. Specific examples of these compounds andmethods for their preparation are provided in U.S. Pat. No. 3,859,379 toKitamura et al.

Suitable curing agents further include polyamine curing agents such as,for example, ethylene diamine, isophorone diamine, cyclohexylenediamine,and a fluorinated diamines such as 4,4′-hexafluoroisopropylidenebis-aniline. In a preferred embodiment, they may be converted from theirusual liquid state into a friable solid that may be pulverized. Afriable, solid, low-temperature curing agent may be selected from ablocked polyamine such as an adduct of an epoxy resin having anequivalent weight of from 400 to 800 AMU and an aliphatic polyaminehaving a primary, secondary, and/or tertiary amino group. The epoxyresin portion of the adduct may be aromatic or aliphatic, as exemplifiedby the bisphenol-based resins mentioned above and the aliphatic analogsthereof, respectively. The cyclohexanol analog of the bisphenol A-basedresin is available under the tradename KUKDO 4100. Higher molecularweight polyamines are preferred when epoxy resins having a lowequivalent weight are employed. Suitable curing agents derived frompolyamines having a primary amino group are available as, for example,HT 835 from Ciba-Geigy and ANCAMINE® 2337 XS from Air Products. An epoxyadduct of an aliphatic polyamine having a secondary amino group, such asANCAMINE® 2014 AS from Air Products, may be preferred for white andlight colored coatings.

Other curing agents that can be used to enhance the curing propertiesinclude dicyandiamide or o-tolyl biguanide. A suitable dicyandiamidecuring agent is sold under the tradename DYHARD® 100M by SKW Chemicals.A suitable o-tolyl biguanide curing agent is sold under the tradenameCASAMINE® OTB by Swan Chemical.

Other suitable curing agents include phenolic curing agents having atleast two terminal hydroxyl groups. Suitable curing agents useful in thepractice of this invention are exemplified by, but are not limited to,phenolic curing agents, such as bisphenol A endcapped diglycidyl etherof bisphenol A, which is the reaction product of diglycidyl ether ofbisphenol A and bisphenol A. Examples of preferred phenolic curingagents for the epoxy resin components include those sold by the DowChemical Company under the tradenames D.E.H.® 87, D.E.H.® 85, andD.E.H.® 84, all of which are believed to be bisphenol A endcappeddiglycidyl ethers of bisphenol A. Other phenolic curing agents includephenol- and cresol-novolac curing agents sold by Georgia Pacific,Reichhold Chemicals and Ciba-Geigy. The curing agent has a hydroxyequivalent weight (HEW) of 180 to 1000 AMU. Within this range, an HEW ofat least 200 AMU may be preferred. Also within this range, an HEW of upto 450 AMU may be preferred.

Mixtures of curing agents may be used. For example a phenolic curingagent may be used in combination with an imidazole such as2-methylimidazole or 2-phenylimidazole pre-dispersed at 0.05 to 5 weightpercent, based on the total curing agent.

When present, the curing agent may be used in an amount of 0.1 to 30parts by weight per 100 parts by weight of the thermoset resin.Selection of a curing agent amount, which may be readily determined bythose of ordinary skill in the art, will depend on the identity of thecuring agent, the identity of the epoxy resin, and the desiredproperties of the cured coating, among other factors.

The composition may, optionally, comprise one or more additives known inthe art. Such additives include, for example, flow control agents, dryflow agents, antioxidants, pigments, optical brighteners, extenders,combinations comprising at least one of the foregoing additives, and thelike.

Examples of the flow control agents include the MODAFLOW® poly(alkylacrylate) products available from Monsanto and the SURFYNOL® acetylenicdiols (e.g., P200), available from Air Products, which contain hydroxyl,carboxyl or other functional groups. The functionalized flow additivesalso aid intercoat adhesion in the event that touch-up or repair of thepowder coating is necessary. The flow additives may be used singly or incombination.

Flow control agents, sometimes called leveling agents, are useful topromote the formation of a continuous coating. Suitable flow controlagents include polyacrylic esters, non-ionic fluorinated alkyl estersurfactants, non-ionic alkylarylpolyether alcohols, silicones, and thelike, and combinations comprising at least one of the foregoing flowcontrol agents. Flow control agents are generally liquids that have beenconverted to powder form by absorption onto silica-type materials. Apreferred flow control agent is sold under the tradename RESIFLOW® P-67acrylic resin by Estron Chemical, Inc., which is a 2-propenoic acid,ethyl ester polymer. Another preferred flow control agent is sold underthe tradename Benzoin by DSM, Inc., which is a2-hydroxy-1,2-diphenylethanone crystalline solid that is believed tokeep the molten coating open for a suitable time to allow outgassing tooccur prior to the formation of the hard set film. When present, theflow control agent may be used at an amount of 1 part by weight to 5parts by weight, per 100 parts by weight of epoxy resin.

Suitable dry flow agents include fumed silica and fumed alumina. Anexample of fumed silica is sold under the tradename CAB-O-SIL® by CabotCorporation. An example of fumed alumina is sold under the tradenameAluminum Oxide C by Degussa Corporation. When present, the dry flowagent may be used in an amount of 0.05 weight percent to 0.5 weightpercent, based on the total weight of the composition.

Pigments may be used to adjust color and opacity. Suitable pigmentsinclude, for example, titanium dioxide, carbon black, phthalocyanineblue, phthalocyanine green, quinacridone red, perylene red, isoindoloneyellow, dioxazine violet, scarlet 3B lake, red 188 azo red, azo pigmentyellow 83, iron oxide pigments, and the like. When present, the pigmentmay be used in an amount of up to 100 parts by weight per 100 parts byweight epoxy resin.

The thermosetting powder coating compositions may contain as anothercomponent, an extender or filler. Suitable extenders include calciumcarbonate, barium sulfate, dolomite, wollastonite, talc, mica, and thelike. When present, the extender may be used in an amount up to 120parts by weight per 100 parts by weight epoxy resin. Within this range,an extender amount of at least 10 parts by weight is preferred. Alsowithin this range, an extender amount of up to 80 parts by weight ispreferred.

Antioxidants prevent discoloration of the coatings. Suitableantioxidants include, for example, sodium hypophosphite,tris-(2,4-di-t-butyl phenyl) phosphite (available as IRGAFOS® 168 fromCiba-Geigy), calciumbis([monoethyl(3,5-di-t-butyl-4-hydroxybenzyl)phosphonate] (available asIRGANOX® 1425 from Ciba-Geigy), and the like. Mixtures of antioxidantsmay be used. The sodium hypophosphite may also act as a buffer againstthe action of trace amounts of chlorine released by epichlorohydrinresidues in the epoxy resins. When present, antioxidants may be used inan amount of 0.5 to 2.0 parts by weight per 100 parts by weight of epoxyresin.

Suitable optical brighteners include, for example,2,2′-(2,5-thiophenediyl)bis[5-t-butylbenzoxazole, available as UVITEX®OB from Ciba-Geigy. When present, optical brighteners may be present at0.1 to 0.5 parts by weight per 100 parts by weight of the epoxy resin.

There is no particular limitation on the method used for forming thecurable composition. Preferred methods include melt mixing, in which thedry ingredients are weighed into a batch mixer and are mixed with amedium intensity horizontal plowmixer or a lesser intensity tumblemixer. Mixing times range from 1 to 3 minutes for the high intensitymixers to 30-60 minutes for the tumble mixers. The premix may then befurther mixed and compounded as the resin is melted in either a singlescrew or a twin screw extruder for 0.5 to 1 minute. The extrudate may becooled quickly and broken into small chips suitable for grinding.

The curable powder coating composition may be used in coating glass,ceramics, and graphite-filled composites, as well as metallic substratessuch as steel and aluminum. The composition is particularly useful inthe coating of heat sensitive substrates such as plastics, paper,cardboard and woods. Wood is herein defined as any lignocellulosicmaterial, whether it comes from trees or other plants, and whether it bein its natural forms, shaped in a saw mill, separated into sheets andmade into plywood, or chipped and made into particleboard, or whetherits fibers have been separated, felted, or compressed. It is exemplifiedby lumber, panels, molding, siding, oriented strand board, hardboard,medium density fiberboard (MDF), and the like. Fiberboard having apattern such as a simulated wood grain printed on its surface, ratherthan on a paper laminated to that surface, and a powder coating of thisinvention over said pattern has the appearance of natural wood. MDF is aparticularly valuable coating substrate. Substrates may preferably havea moisture content of 3 to 10% by weight. The substrate may be treatedto enhance its electrical conductivity. Thus, a porous substrate such asparticleboard, pre-coated with a conductive liquid coating compositionand cured, may also serve as a substrate for the coating powder. Forexample, a smooth 2-3 mil thick powder coating is achieved on a 0.5 to 1mil thick UV-cured or thermally cured pre-coat. The curable powdercoating composition is also useful for coating plastic parts for theinterior and exterior of automobiles.

The coating powder may be applied to substrates by conventional means,including electrostatic fluidized beds, electrostatic spray guns,triboelectric guns, and the like. The coating thickness may be 1.0 milto 25 mils. Within this range, a coating thickness of at least 1.5 milsis preferred. Also within this range, a coating thickness of up to 4mills is preferred.

The curing temperature may be 200° F. to 500° F. Within this range, thecure temperature may preferably be at least 220° F., more preferably atleast 250° F. Also within this range, the cure temperature maypreferably be up to 450° F., more preferably up to 400° F. One advantageof the curable compositions is their ability to produce matte and lowgloss finishes at low curing temperatures, such as curing temperaturesas low as 350° F., more preferably as low as 300° F., even morepreferably as low as 250° F. Another advantage of the curablecompositions is their ability to produce matte and low gloss finishesover a wide range of curing temperatures. For example, such finishes maybe produced over the entire temperature range of 300° to 400° F., morepreferably 250° F. to 400° F.

One embodiment is a curable powder coating composition, comprising: 100parts by weight of a bisphenol A epoxy resin; 5 to 20 parts by weight ofa partially monoesterified styrene-maleic anhydride resin having a glasstransition temperature less than 105° C. and an acid number of greaterthan 110 mg KOH/g; and 1 to 6 parts by weight of an imidazole curingagent.

Another embodiment is a cured powder coating composition, comprising thereaction product of: an epoxy thermoset resin; and a matting agentselected from styrene-maleic anhydride copolymers having a glasstransition temperature less than 105° C. Another embodiment is anarticle comprising the above cured powder coating composition.

Another embodiment is a method of forming a cured powder coating,comprising: heating a curable powder coating composition at atemperature up to 350° F. and a time up to 60 minutes to form a curedpowder coating exhibiting a 60° gloss value less than 30 units measuredaccording to ASTM D523; wherein the curable powder composition comprisesan epoxy thermoset resin, and a styrene-maleic anhydride copolymerhaving a glass transition temperature less than 105° C.

Another embodiment is a method of forming a cured powder coating,comprising: heating a curable powder coating composition at atemperature of 250° F. to 400° F. and a time of 1 minute to 60 minutesto form a cured powder coating exhibiting a 60° gloss value less than 30units measured according to ASTM D523; wherein the curable powdercomposition comprises an epoxy thermoset resin, and a styrene-maleicanhydride copolymer having a glass transition temperature less than 105°C.; and wherein the specified gloss is obtained throughout the curingtemperature range of 250° F. to 400° F.

The invention is further illustrated by the following non-limitingexamples.

General Experimental

All components were obtained commercially. A diglycidyl ether ofbisphenol A epoxy resin with a weight per epoxide between 650 and 725grams was obtained as ARALDITE® GT-7013 is from Vantico. A diglycidylether of bisphenol A epoxy resin with a weight per epoxide between 550and 700 grams was obtained as ARALDITE® GT-7072 from Vantico. Animidazole adduct with a diglycidyl ether of bisphenol A epoxy resin wasobtained as ARALDITE® HT 3261 from Vantico. A mono-salt of apolycarboxylic acid and a cyclic amidine was obtained as VESTAGON® B68from Creanova, Inc. An acrylic flow modifier absorbed onto silica gelwas obtained as RESIFLOW® P-67 from Estron Chemical. Inc. Barium sulfatewas obtained as Barite 1075 from Polar Minerals. Carbon black pigmentswere obtained as Raven Black 22, Raven Black 500, Raven Black 1250Beads, and Raven Black 1255 from Columbian Chemicals, Inc. Calciumcarbonate was obtained as QUINCY WHITE® 6 from Omya.

A fumed silica was obtained as CAB-O-SIL® M5 from Cabot Corporation. Afumed alumina was obtained as Aluminum Oxide C from Degussa. Asubstituted dicyandiamide was obtained as DYHARD® 100M from SKWChemicals, Inc. 2-Methyl imidazole was obtained as DYHARD® MI from SKWChemicals, Inc. 2-Hydroxy-2-phenylacetophenone was obtained as Benzoin Mis from DSM.

A partially monoesterified styrene-maleic anhydride copolymer wasobtained as SMA® 1440F from Sartomer; this material has a styrene:maleicanhydride mole ratio of 1:1, a glass transition temperature of 55° C.,an acid number of 165-205, 55-75% monoesterification, and meltviscosities of 300 poise at 160° C., 110 poise at 180° C., and 70 poiseat 200° C. A styrene-maleic anhydride copolymer was obtained as SMA®3000A from Sartomer; this material has a styrene:maleic anhydride moleratio of 3:1, a glass transition temperature of 125° C., an acid numberof 285, and melt viscosities of 17,300 poise at 180° C., 1,650 poise at200° C., and 300 poise at 200° C. A partially monoesterifiedstyrene-maleic anhydride copolymer was obtained as SMA® X.10840 fromSartomer; this material has a styrene:maleic anhydride mole ratio of1:1, a number average molecular weight of 2,640 AMU, a weight averagemolecular weight of 5,600 AMU, a glass transition temperature of 85° C.,an acid number of 240, 65% monoesterification, and viscosities of 1,700poise at 160° C., 420 poise at 180° C., and 140 poise at 200° C. Apartially monoesterified styrene-maleic anhydride copolymer was obtainedas SMA® X.11825 from Sartomer; this material has a styrene:maleicanhydride mole ratio of 1:1, a glass transition temperature of 110° C.,an acid number of 315, 25% monoesterification, a weight averagemolecular weight of 3,200 AMU, and a number average molecular weight of6,800 AMU. A partially esterified styrene-maleic anhydride copolymer wasobtained as SMA® 11850 from Sartomer; this material has a styrene:maleicanhydride mole ratio of 1:1, a glass transition temperature of 90° C.,an acid number of 215, 50% monoesterification; a number averagemolecular weight of 3,800 AMU, and a weight average molecular weight of8,300 AMU. A partially monoesterified styrene-maleic anhydride copolymerwas obtained as SMA® 31890; this material has a styrene:maleic anhydridemole ratio of 3:1, a glass transition temperature of 45° C., an acidnumber of 110, 85% monoesterification, a number average molecular weightof 6,200 AMU, a weight average molecular weight of 15,000 AMU, andviscosities of 150 poise at 140° C., 40 poise at 160° C., and 20 poiseat 180° C. A styrene-maleic anhydride copolymer was obtained as SMA®EF32 from Sartomer; this material has a glass transition temperature of123° C., and acid number of 285, and viscosities of 1,110 poise at 160°C., 165 poise at 180° C., and 35 poise at 200° C. A styrene-acrylic acidcopolymer was obtained as MOREZ® 101 from Rohm and Haas Company; thismaterial has a glass transition temperature of 93° C. and an acid numberof 205. A styrene-acrylic acid copolymer was obtained as SCX-848 fromJohnson Polymers; this material has a glass transition temperature of67° C., an acid number of 215, a number average molecular weight of1,419 AMU, a weight average molecular weight of 4,572 AMU, and aviscosity of 23 poise at 200° C.

Unless otherwise noted, all component amounts are expressed as parts byweight.

Coating powders were prepared by initially blending by hand for 1 minuteall components except the fumed alumina or fumed silica. The blend wasthen melt mixed in a 30 mm twin screw Baker Perkins extruder having afront zone maintained at 180° F. and an unheated rear zone. Theextrudate was then chipped and ground with 0.1-0.2% by weight of fumedalumina or fumed silica to a fine powder that passed through a 140 meshscreen (U.S. Standard).

Pre-cleaned steel test panels (from “Q” Panel Co.) measuring3″×6″×0.032″ (7.6×15.2×0.08 cm) were coated using standard electrostaticspray techniques and baked in an oven at the temperatures and timesspecified to give a coating having thickness of 1.5 to 2.5 mils.

Forward impact resistance was measured according to ASTM G 14 using a ⅝″indenter.

Methyl ethyl ketone resistance (MEK resistance), a rating of solventresistance and an indication of crosslink density, was measured asfollows. A cotton swab was soaked in MEK and rubbed with pressure in aback and forth stroking motion 50 times. A relative rating was given ona scale of 1-5 with a rating of 5 defined as the most solvent resistantand a rating of 1 justified when the coating can be completely removedduring the process to expose bare substrate. More specifically, a ratingof 5 corresponds to no rub off, 4 to slight rub off, 3 to moderate ruboff, 2 to severe rub off, and 1 to complete rub through to substrate.

Gloss was measured at 60° according to ASTM D523.

COMPARATIVE EXAMPLE 1

The composition of Comparative Example 1 is given in Table 1. Testresults, presented in Table 4, show that a matte finish can be obtainedif cure is carried out at temperatures of 300° F. or above. However,below 300° F. the coating system does not adequately cure, even whencuring times are extended to 60 minutes. As a result the final surfacegloss is dependent on curing temperatures varying from 10 to 100 unitsas temperatures vary from 250-300° F. Similar coatings are described inProduct Literature from Ciba under the title, “Matting Agents/Hardenersfor Powder Coatings” (1998). In this literature Ciba teaches a minimumcure schedule of 356° F. (180° C.) for 20-25 minutes.

TABLE 1 Comp. Ex. 1 ARALDITE ® GT-7013 100 VESTAGON ® B68 9 RESIFLOW ®P-67 1.4 Barite 1075 100 Raven Black 22 3 CAB-O-SIL ® M5 0.1

EXAMPLES 1-4, COMPARATIVE EXAMPLES 2-7

The compositions of Examples 1-4 and Comparative Examples 2-7 are givenin Table 2. Test results are presented in Table 4.

Comparative Example 2 lacked any reactive matting agent. High gloss wasachieved at 250, 300 and 400° F. curing temperatures.

Comparative Examples 4 and 5 illustrate the use of styrene acrylic acidcopolymers, which are conventional reactive matting agents used toreduce surface gloss in epoxy resins. For these Comparative Examples,60° gloss varied significantly with cure temperature, ranging from theteens to greater that 50 units over the curing temperature range of250-400° F.

Comparative Examples 3, 6 and 7 utilized styrene-maleic anhydridecopolymers or esterified styrene-maleic anhydride copolymers as reactivematting agents. For Comparative Example 3, results show that when usingSMA® 3000A a matte finish was achieved when cure reactions are carriedout at a temperature of 400° F.; however, a matte finish was notachieved at temperatures less than 300° F., with the reported 60° glossof 60 units for a curing temperature of 250° F. Results for ComparativeExamples 6 and 7 show that SMA® 31890 and SMA® EF32 were not veryeffective matting agents even at high temperatures. For example, whencuring was carried out at 400° F., 60° gloss values of 33 and 45 unitswere obtained with SMA® 31890 and SMA® EF32, respectively.

Examples 1-4 utilized particular partially monoesterified styrene-maleicanhydride copolymers having glass transition temperatures of 110° C. orless. Each of Examples 1-4 demonstrated the ability to provide a matteepoxy finish at cure temperatures of less than 300° F. The also provideda more consistent surface appearance when curing temperatures variedfrom 250 to 400° F. For instance, Example 4 provided a surface 60° glossranging from 3-7 units as cure temperatures ranged from 250-400° F. Overthis same temperature range Examples 1-3 provided 60° gloss ranges of6-19, 4-14, and 9-17 units, respectively.

TABLE 2 C. Ex. 2 C. Ex. 3 C. Ex. 4 C. Ex. 5 ARALDITE ® GT-7013 100 100100 100 DYHARD ® 100 M 4 4 4 4 DYHARD ® MI 0.8 0.8 0.8 0.8 RESIFLOW ®P-67 2 2 2 2 Benzoin M 0.8 0.8 0.8 0.8 Barite 1075 20 20 20 20 Raven1255 4 4 4 4 SMA ® 3000 A — 20 — — MOREZ ® 101 — — 20 — SCX-848 — — — 20Aluminum Oxide C 0.2 0.2 0.2 0.2 C. Ex. 6 C. Ex. 7 Ex. 1 Ex. 2ARALDITE ® GT-7013 100 100 100 100 DYHARD ® 100 M 4 4 4 4 DYHARD ® MI0.8 0.8 0.8 0.8 RESIFLOW ® P-67 2 2 2 2 Benzoin M 0.8 0.8 0.8 0.8 Barite1075 20 20 20 20 Raven 1255 4 4 4 4 SMA ® EF 32 20 — — — SMA ® 31890 —20 — — SMA ® 10840 — — 20 — SMA ® 11825 — — — 20 Aluminum Oxide C 0.20.2 0.2 0.2 Ex. 3 Ex. 4 ARALDITE ® GT-7013 100 100 DYHARD ® 100 M 4 4DYHARD ® MI 0.8 0.8 RESIFLOW ® P-67 2 2 Benzoin M 0.8 0.8 Barite 1075 2020 Raven 1255 4 4 SMA ® 11850 20 — SMA ® 1440F — 20 Aluminum Oxide C 0.20.2

EXAMPLES 5-7, COMPARATIVE EXAMPLE 8

The compositions of Examples 5-7 and Comparative Example 8 are given inTable 3. Results are presented in Table 4. Example 5 demonstrates theuse in epoxy systems of a reactive matting agent in which an imidazoleadduct is used as the curing agent. In this example, the surface 60°gloss ranges from 5-9 as the curing temperature varies from 250° F. to400° F. This same system without reactive matting agent, shown inComparative Example 8, exhibits high gloss over the same curingtemperature range. Example 6 demonstrates the ability to achieve lowgloss, rather than matte, surface finishes when curing is carried out attemperatures of 250° F. by simply adjusting the level of reactivematting agent. In other words, one can select a gloss finish by simplyadjusting the amount of the matting agent. A comparison of Example 5 andExample 7 illustrates the ability to obtain improved impact propertiesand improved insensitivity of gloss to cure temperature.

TABLE 3 C. Ex. 8 Ex. 5 Ex. 6 Ex. 7 ARALDITE ® GT-7013 100 100 50 50ARALDITE ® GT-7072 — — 50 50 ARALDITE ® HT-3261 4.5 4.5 4.5 4.5RESIFLOW ® P-67 2 2 1.4 1.4 Barite 1075 20 20 — — QUINCY WHITE ® 6 — —30 20 Raven Black 1255 4 4 — — Raven Black 1250 Beads — — 2 — RavenBlack 500 — — — 2 SMA ® 1440F — 20 9 15 Aluminum Oxide C 0.2 0.2 0.2 —CAB-O-SIL M5 — — — 0.1

TABLE 4 Cure Temperature Cure Time 60° gloss Forward Impact MEKresistance (° F.) (minutes) units (in.-lbs.) (1-5 rating) C. Ex. 1 40015 2 100 4 375 15 3 100 3 350 30 3 100 3 300 45 10 60 2 275 60 42 20 2250 60 100 fail 1 C. Ex. 2 400 8 98 160 4 300 15 98 160 4 250 20 104 1604 C. Ex. 3 400 8 6 100 4 300 15 18 80 4 250 30 60 60 3 C. Ex. 4 400 1012 40 4 350 12 11 — 4 300 15 15 20 4 275 20 25 40 3 250 30 65 60 2 C.Ex. 5 400 8 17 40 4 350 12 21 40 4 300 15 29 40 3 275 20 40 20 3 250 3057 20 2 C. Ex. 6 400 8 45 40 4 300 15 39 — — 250 30 58 — — C. Ex. 7 4008 33 60 4 300 15 38 60 4 250 30 60 40 3 Ex. 1 400 8 6 20 4 350 12 7 20 4300 15 7 40 4 275 20 14 40 3 275 30 14 40 4 250 30 18 40 2 250 45 19 404 Ex. 2 400 8 4 20 4 350 12 4 20 4 300 15 5 40 3 250 30 14 20 2 Ex. 3400 8 10 20 4 350 12 10 20 4 300 15 9 20 4 275 20 11 40 3 250 30 17 20 3Ex. 4 400 8 3 40 4 350 12 3 40 4 300 15 3 40 3 275 20 4 40 3 250 30 7 402 250 45 6 80 3 C. Ex. 8 400 8 98 160 5 350 12 99 160 5 300 15 97 160 5275 20 97 160 4 250 30 96 160 4 Ex. 5 400 8 5 120 4 350 12 5 100 4 30015 5 60 4 275 20 7 60 4 250 30 9 40 3 Ex. 6 250 30 30 140 4 Ex. 7 400 83 140 5 325 10 3 160 4 300 15 3 100 4 300 20 3 160 4 275 20 3 140 5 25030 5 140 4

While the invention has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing fromessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. A curable powder coating composition, comprising: an epoxy thermosetresin; and a styrene-maleic anhydride copolymer having a glasstransition temperature less than 105° C. and having an acid number offrom 110 mg KOH/g to 210 mg KOH/g.
 2. The curable powder coatingcomposition of claim 1, wherein the thermoset resin is a bisphenol Aepoxy resin.
 3. The curable powder coating composition of claim 1,wherein the styrene-maleic anhydride copolymer comprises a partiallymonoesterified styrene-maleic anhydride resin.
 4. The curable powdercoating composition of claim 1, wherein the styrene-maleic anhydridecopolymer has a mole ratio of styrene:maleic anhydride of 1:1 to 4:1. 5.The curable powder coating composition of claim 1, comprising 3 to 30parts by weight of the styrene-maleic anhydride copolymer per 100 partsby weight of the epoxy thermoset resin.
 6. The curable powder coatingcomposition of claim 1, further comprising a curing agent.
 7. Thecurable powder coating composition of claim 6, wherein the curing agentcomprises an imidazole having the formula

wherein R¹-R⁴ are each independently hydrogen, C1-C12 alkyl, C6-C18aryl, C7-C18 arylalkyl, and C7-C18 alkylaryl.
 8. The curable powdercoating composition of claim 1, further comprising an additive selectedfrom the group consisting of flow control agents, dry flow agents,antioxidants, pigments, optical brighteners, extenders, and combinationscomprising at least one of the foregoing additives.
 9. The curablepowder coating composition of claim 1, wherein the composition aftercuring exhibits a 60° gloss value less than 30 units measured accordingto ASTM D523.
 10. The curable powder coating composition of claim 1,wherein the composition is curable at a temperature less than 300° F. toform a surface having a 60° gloss value less than 30 units measuredaccording to ASTM D523.
 11. The curable powder coating composition ofclaim 1, wherein curing the composition at any temperature in the rangeof 300° F. to 400° F. produces a 60° gloss value less than 30 unitsmeasured according to ASTM D523.
 12. A curable powder coatingcomposition, comprising: 100 parts by weight of a bisphenol A epoxyresin; 5 to 20 parts by weight of a partially monoesterifiedstyrene-maleic anhydride resin having a glass transition temperatureless than 105° C. and an acid number of greater than 110 mg KOH/g and upto 210 mg KOH/g; and 1 to 6 parts by weight of an imidazole curingagent.
 13. A cured powder coating composition, comprising the reactionproduct of: an epoxy thermoset resin; and a matting agent selected fromstyrene-maleic anhydride copolymers having a glass transitiontemperature less than 105° C. and an acid number of greater than 110 mgKOH/g and up to 210 mg KOH/g; and, a curing agent chosen from an epoxyadduct of an imidazole, 2-phenyl imidazole, and a block polyamine. 14.An article comprising the cured powder coating composition of claim 13.15. A method of forming a cured powder coating, comprising: heating acurable powder coating composition at a temperature up to 350° F. and atime up to 60 minutes to form a cured powder coating exhibiting a 60°gloss value less than 30 units measured according to ASTM D523; whereinthe curable powder composition comprises an epoxy thermoset resin, and astyrene-maleic anhydride copolymer having a glass transition temperatureless than 105° C. and an acid number of greater than 110 mg KOH/g and upto 210 mg KOH/g; and, a curing agent chosen from an epoxy adduct of animidazole, 2-phenyl imidazole, and a block polyamine.
 16. A method offorming a cured powder coating, comprising: heating a curable powdercoating composition at a temperature of 250° F. to 400° F. and a time of1 minute to 60 minutes to form a cured powder coating exhibiting a 60°gloss value less than 30 units measured according to ASTM D523; whereinthe curable powder composition comprises an epoxy thermoset resin, and astyrene-maleic anhydride copolymer having a glass transition temperatureless than 105° C., and an acid number of from 110 mg KOH/g to 210 mgKOH/g; and wherein the specified gloss is obtained throughout the curingtemperature range of 250° F. to 400° F.